Process for the solvent extraction of lubricating oils



25, 1937. D. R. MERRILL 2,081,495

PROCESS FOR THE SOLVENT EXTRACTIQN 0F LUBRICATING OILS Filed Dec. 5, 1935 Patented May a 25, 1937 UiiiTED STATES PROCESS FOR THE SOLVENT EXTRACTION l F LUBRICATING OILS David R. Merrill, Long Beach, Calif., assignor to Un on Oil Company of California, Los Angeles, Calif., a corporation of California Application December 5, 1933, Serial No. 701,016

9 Claims.

This invention relates to a process for the treatment of petroleum with selective solvents.

In the production of lubricating oil from crude petroleum residues or distillates, it is becoming conventional in the art to separate the desirable parafiinic hydrocarbons from the undesirable olefinic, naphthenic and/0r aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons but which exhibit 1 only a very limited solvent power for the desirable paraifinic hydrocarbons.

When I use the term paraffinic hydrocarbons" I mean those relatively highly saturated com-' pounds which are present in petroleum charac- 15 terized by a low temperature viscosity susceptibility, i. e., they exhibit a minimum change in viscosity for a given change in temperature, and characterized by relative stability to air and sunlight, exhibiting little tendency toward discolor- 20 ation or sludge formation. This definition is not meant to include those compounds which are usually solid or semi-solid at ordinary temperatures and which are known as "wax" or petrolatum. As a matter of convenience hereafter, 25 I will refer to the undesirable components, such as olefinic, naphthenic and/ or aromatic hydrocar- $611903 viscosity gravity constant for an extreme Gulf Coast type to 0.807 for an extreme Pennsylvania type, or even beyond. The viscosity gravity constant referred to in this application has been determined by the method employed by Hill 45 and Coates as set forth in the Journal of Industrial and Engineering Chemistry, vol. 20, page 641 of 1928. I A number of selective solvents for this purpose have been found; for example, it has been shown 50 that such materials as liquid sulphur dioxide,

beta beta dichlorethyl ether, chloraniline, nitrobenzene, aniline and furfural are highly selective as solvents for the non-paraflinic hydrocarbons. These solvents may be used alone or modified by 56 the presence of such agents as carbon bisuiphide,

xylene, benzene, toluene, carbon tetrachloride,

v ethers, tetrachlor-ethane or the like. When these relatively heavy solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable 5 non-parafiinic hydrocarbons pass into solution to a greater or less extent but the desirable parafflnic hydrocarbons remain largely undissolved. The solution of undesirable hydrocarbons and solvent settles to the bottom of the container and forms what is known as an extract phase. The relatively light parafiinic hydrocarbons rise to the top of the vessel and form a raflinate phase. These phases are then readily separable by ordinary decantation means. The rafiinate phase is usually found to contain a small quantity of the selective solvent and the extract phase ordinarily contains a relatively large quantity of the solvent. These fractions may be purified by distillation whereby the solvent is distilled away from the hydrocarbon oils.

Due to the general similarity of the various hydrocarbon components of mineral oil fractions such as lubricating oils, solubilities of the undesirable, non-parafilnic fractions and of the desirable parafllnic fractions in a selective solvent usually differ only in degree and there is, therefore, a tendency for desirable, high grade paraffinic oil to be carried away with the extract resulting in a loss in the yield of paramnic fractions obtained. In other words, in a phase separation of extract and raffinate fractions from mineral oil employing a selective solvent, an equilibrium of paraflinic components as well as non-paraffinic components is established between the phases. Consequently, some of the desirable paramnic fraction is found in the extract instead of in the raflinate.

It is an object of my invention to reduce the loss of these valuable components in the extract phase.

In producing a high quality final raflinate from a stock containing a limited quantity of such raflinate, it is necessary to dissolve and carry away a large proportion of the original feed. In 5 the case of many solvents, such as dichlorethyl ether, and to an even greater extent liquid sulphur dioxide alone or modified with benzene, the solubility of the oil in the extract phase even at temperatures within 5 F. or 10 F. of the miscim bility temperature is rather limited. In consequence, it is necessary in refining such stock for the production of low viscosity gravity constant oils to use a large proportion of solvent to feed stock in order to remove in solution from I 2 I accuses separation can take place and the better is the quality of the'ramnate thus obtained. The temperature of complete miscibility of all the oil with the solvent in any stage of extraction is a function of both the average composition of the oil in that stage, including the oil in both phases, and the proportion of total solvent to total oil in that e.

In operation on an oil containing a substantial proportion of oils of highly aromatic or non-pan afinic character and very high viscosity gravity constant, dimculty has been encountered from miscibility in attempting to operate the feed stage at the desired high temperature. For instance, with dichlorethyl ether, miscibility was encountered in attempting to operate the feed stage at 120 F. and it has been found necessary to lower this temperature to about 80 to 85 F. in order to avoid complete miscibility at this point and thus permit practical operation. While using such comparatively low temperatures at the feed stage, it is evident that the extraction at this point is reduced and it has been found necessary to employ somewhat larger proportions of solvent to produce a final rafllnate of the desired quality. It is therefore desirable to treat such highly aromatic oils, for instance, Kettleman Hills deasphaltlzed' and dewaxed long residuum having a viscosity gravity constant of 0.87, by a preextraction to remove the highly aromatic oils to a greater or less extent before proceeding with the extraction to separate the oils of very low viscosity gravity constant from those characterized by intermediate viscosity gravity constant.

While it is evident that such a pre-extraction can be accomplished as an entirely separate operation with solvent of either the same or a different type from that employed in the subsequent extraction, the additional solvent requirements increase the expense or operation.

oil and'solvent passes through orifice mixer l5 and line I 6 into separator I'I. Rafllnate phase from separator l1 exits via line l8 controlled by valve l9 by action of pump 20 and passes with extract phase trom extractor I00, to be described, through orifice mixer 2| and line 22 into 1a. section or extraction column 25. In this column the oil .passes countercurrently with a selective solvent brought from tank 26 via line 2'! controlled by valve 28 by action or pump 29, via line 30 controlled by valve 3!, through orifice mixer 32 and via line 33. High grade rafllnate is removed from column 25 through line 35 controlled by valve 38. Extract phase is removed from column 25 through line 3'! controlled by valve 38 by action of pump 39. Column 25 comprises sections to 41 separated by imperiorate plates 50. Each section comprises a mixing zone 5! and a settling zone as separated by plate '53 provided with port as.

Separator 57, described above, is likewise divided into similar zones. I

Connected with sections til to as are lines 55 p with valves 56 and pumps 5? to remove the extract phases from these sections and lines 58 with valves 59 and pumps 56 are provided to remove the rafiinate phases therefrom. The ex tract phases from upper sections are commingled in lines ti with the rafilnate phases from lower sections and the mixtures are passed through orifice mixers 52 and lines 68 intothe respective intermediate sections. The raifinate phase from section ts is removed therefrom by action of pump 61! through line 65 controlled by valve 56 and is intermixed in line 38 with fresh solvent entering column 25.

In the above-described apparatus, solvent is introduced into the upper section of extractor 25,

for example section at and the oil is introduced into a lower or tertiary section, for instance section 615. Extraction takes place in all sections and the extract phase from the upper section is commingled in the intermediate or secondary section, for example. section 36 with the rafllnate produced in the lower section. Raflinate from the intermediate section travels to the upper section and extract from the intermediate section passes to the lower section.

Because of the magnitude of the partition 00- eiiicient of parafllnic constituents between the rafiinate and extract phases in any one section, the presence of the highly paraflinic raffinate results in substantial proportions of the paramn'ic components passing into the extract phase. By intermixing the less paraiilnic raflinate, for instance from section 45 with the extract phase from section 47 containing a relatively high proportion of parafilnic materials and causing a. phase separation as in section 46, at least a portion of the parafllnic fractions will pass from the extract into the rafllnate.

By contacting an extract-solvent mixture from Q an upper section of the tower with a rafllnate from a lower section, a redistribution or paraflinic fractions takes place. The extract-solvent mixture contains so large a. proportion of parailinic hydrocarbons and the rafllnate from a lower section contains relatively so small a, proportion of these hydrocarbons that when said extract and said rafiinate are mingled in the presence of the solvent, sufficient paraflinic fractions pass.

from the extract to the rafllnate to establish-equilibrium between the two phases. Also. at the same time, some or the-non-paraflinic' fractions pass from the raflinate to the extract, resulting in a more paraflinic rafilnate and a. less par! afllnic extract. Consequently, after a. succession of such steps, the final extract contains the least amount '01 paraflln fractions and the final rafllnate contains those parafll'nlc fractions which are normally lost in the extract. The solvent associated with the' extract. and rafllnate can. be removed therei'romby usual means such as by distillation.

'Extract phase issuing from column 25 through line 3] is passed through cooler I0 where its temperature is reduced suillciently to cause phase separation in separator II to which it passes through line I2. Rejected rafllnate phase insoluble under the conditions existing in separator H is passed through line 13 controlled by valve 14 by action of pump 15 into contact with extract phase from section 4| and theme is introduced into rectification section 40 via line GI, orifice mixer 62 and line 63. Extract phase in separator II is removed therefrom by action of pump 78 via line I6 controlled by valve TI. This raflinate passing through the rectification stage hecomes enriched in high grade components and loss of these valuable fractions in the extract phase is thus reduced.

Returning to the first stage of extraction in separator II, the extract phase is removed therefrom via line 80, valve 8| and pump 82 and thence passes through cooler 83 where its temperature is suificiently reduced to cause a rejection of oil in separator 85 to which the stream passes through line 85. Low grade extract is removed from separator 85 through line 86 controlled by valve 81. The rejected oil from 85 may contain a substantial proportion of parafiinic oil and may be forced by pump 80 through lines 89 and 90 and valve i into intermixture with the primary rafiinate from separator I? which passes through line 80 on its way to section SI of column 25.

If desired, the rejected oil from separator may pass through line 89 and valve 92 into contact with the extract phase produced in separator H passing through line I0. This mixture then travels through orifice mixer 95 and line 95 into extractor I00 in which it is counter-currently extracted with a selective solvent from tank 26 passing through lines 21 and 30, valve IOI, orifice mixer I02 and line I03. An intermediate grade raffinate is removed from extractor I00 via line I00 controlled by valve I05. Extract phase travels from extractor I00 by action of pump I06 through line I07 controlled by valve I00 and passes through cooler I09 wherein its temperature is reduced sufiiciently to cause phase separation in separator I I0 to which it passes through line I II. Rejected oil is removed by pump IIZ through line H3 and valve H0 and is returned into column I00 for rectification in a manner similar to the rectification of the rejected oil from separator II in rectification-zone 60 of column 25. Extract phase comprising contaminated solvent from separator II 0 passes through line I G, valve H5 and pump II6 into admixture with oil feed passing through line I0 for extraction in the manner above described. Preferably, temperature conditions in separator I I0 will be such that the extract phase removed via line I 4 will comprise solvent contaminated with 8'% or less oil.

Extractor I00, like column 25, is divided into' a. number of sections I20, I2I and I22, comprising mixing zones 5|, settling zones 52 and plates 53 provided with ports 54. Extract phase from section I22 is intermixed with rafiinate phase from section I20 and the mixture is passed into the intermediate section I2I in a manner similar to the flow of material in column 25. Rafllnate phase from section I2I passes into section I22 to- .gether with fresh solvent by flow through line I23, valve I25, pump I25, line 30, orifice mixer I02 and line I03. Extract phase in section I2I is forced by action of pump I25 in line I21 through valve I28 and line I29 into contact with the, above described mixture flowing through line It. Or, if desired, the extract phase may travel from section I 2| through line I21 and valve I30 into admixture with the above described oil passing through line I8 from separator I1.

As an example of the operation of this apparatus, the above-described Kettleman Hills deasphaltized and dewaxed long residuum characterlled by a viscosity gravity constant of about 0.87 was extracted with a selective solvent comprising 75% liquid sulphur dioxide and 25% benzene. The oil feed was extracted in the first stage in separator II at 40 F. The extract phase from section 41. Section I into which the oil was introduced from separator H was maintained at 105 F. This temperature is appreciably below the miscibility temperature after said pre-extraction has removed a substantial portion of the highly aromatic fractions.

Extract phase from column 25 was cooled to 80 F. in cooler I0 to cause phase separation in separator II. The temperature in extractor I00 was progressively increased from 60 F. in section I20 to 80 F. in section I22. The extract phase from extractor I00 was cooled to 20 F. in cooler I 09 in order to cause rejection of a ramnate in separator H0. About 250 volume percent. of solvent to oil introduced into the system was employed in column 25 and an additional amount of solvent to the extent of 40 volume percent. was

introduced into extractor I00. The contaminated solvent from separator IIO was used as the selective solvent for the primary extraction in separator I'Ir In my invention above described, the valuable parafiinic components norm'ally lost in the extract phase are recovered in the rafllnate phases and the pre-extraction in separator I1 is accomplished by a recovered solvent from another stage of the extraction system. It is to be understood that the stages shown may be either entirely separate stages or merely regions of a continuous extractor in which different temperatures are maintained. Also, the temperatures set forth are merely by way of illustration and may be varied for other stocks and solvents. Furthermore, the number of stages shown in the figures is to be considered merely typical for these general conditions and. may be varied as desired. Thus,

more rectification stages may be employed and the number of extraction stages may be increased or decreased as is found desirable in any particular circumstance.

My invention is capable of many modifications and variations as will be apparent to those skilled in the art within the scope of the following claims.

I claim:

l. A process for the separation of paraflinic and non-paraflinic fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent, separating insoluble ramnate from the extract phase, cooling said extract phase to separate a rejected oil therefrom, extracting said rejected oil with a selective solvent, cooling the extract phase from said last mentioned extraction to separate a rejected oil therefrom, returning the last mentioned rejected oil to said last mentioned extraction to rectify the same and returning extract phase from said last mentioned cooling to said first mentioned extraction to operate as a selective solvent therein.

2. A process for the separation of parafllnic and non-parafiinic fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent to separate an insoluble raffinate from the extract phase, cooling mentioned extraction to separate a rejected oil from contaminated solvent, returning said contaminated solvent to said first mentioned extraction to operate as a selective solvent thereinand.

further extracting the ramnate from said first mentioned extraction with selective solvent to produce a high quality ramnate and an intermediate I grade extract therefrom.

3. A process for the separation of paramnic and non-parafilnic fractions from' mineral oil containing the same which comprises extracting said oil with a selective solvent to separate an insoluble ramnate from the extract phase, subjecting said rafdnate to a second extraction with a selective solvent to produce a high'quality rafflnate and an intermediate grade extract therefrom, cooling said intermediate grade extract to separate a rejected oil from contaminated solvent, cooling the extract phase from said first mentioned extraction to separate a rejected oil therefrom and extracting said last mentioned rejected oil with said contaminated solvent.

4. A process for the separation of paramnic and non-paramnic fractions from mineral oil containing the same which comprises extract ing said oil with a selective solvent to separate an insoluble rafinate from the extract phase, subjecting said raifinate to a second extraction with a selective solvent to produce a high quality and non-paraflinic fractions from mineral oil containing the same which comprises extracting said 011 with a. selective solvent to separate an insoluble rafflnate from the extract phase, subjecting said raflinate to a second extraction with a selective solvent to produce a high quality rafflnate and an intermediate grade extract therefrom, cooling said intermediate grade extract to separate a rejected oil from contaminated.

solvent, returning said rejected oil to said sec- 0nd extraction'to' rectify the same,-cooling the extract phase from said first mentioned extracaoei eee tion to separate a rejectedoii theretrom and extracting said last mentioned rejected oil with Y said contaminated solvent.

6. A process for the separation of pane and non-paraflinic fractions from mineral oil containing the same which comprises extract.- ing said oil with a selective solvent to separate an insoluble raflinate from the extract phase,

phase.

7. A process for the separation of parafinic and non-parafiinic fractions from mineral 611 containing the same which comprises extracting said oil with a selective solvent to separate an insoluble ramnate from the extract phase, cooling said extract phase to separate a rejected oil therefrom, mixing said last mentioned rejected oil with said first mentioned ramnate, extracting said mixture with a selective solvent to pro- I duce a high grade rafiinatc and an intermediate extract phase and returning said intermediate extract phase to said first mentioned extraction to operate as a solvent therein.

- 8. A process for the separation of oil into fractions with a selective solvent which comprises commingling said oil with a selective solvent and thereby producing'an extract phase and a raffinate phase, separating said phases, passing said rafiinate phase to a second extraction stage and commingling said raflinate phase passed to said second extraction stage with a selective solvent, thereby producing a. final raflinate phase and a second extract phase, separating said phases, cooling said second extract phase and thereby causing a portion of the relatively more parafflnic oil presentrin 'saidsecond extract phase to be forced out of solution, separating the oils forced out of solution by cooling said second extract phase from the remaining oils dissolved in said second extract phase and returning said oils forced out of solution by cooling said second extract phase to said second extraction stage.

9. A process as claimed in claim 8 in which DAVID R. MERRIIL. 

